U.S. Pat. No. 6,377,034 discloses a configuration of a current detection circuit which detects a current flowing through a drive circuit.
Specifically, the current detection circuit is a circuit for detecting a current flowing through an N-channel drive transistor provided on a high side of the drive circuit. The current detection circuit has at least a sense transistor, an operational amplifier, and a transistor. The sense transistor has a drain and a gate which are coupled respectively to a drain and a gate of the drive transistor. The operational amplifier amplifies a potential difference between a source voltage of the sense transistor and a source voltage of the drive transistor. The transistor is coupled in series with the sense transistor, and has a gate to which an output voltage of the operational amplifier is supplied.
A gate-source voltage and a drain-source voltage of the sense transistor respectively indicate the same values as a gate-source voltage and a drain-source voltage of the drive transistor. Thus, through the sense transistor, a current (for example, a current of one thousandth) proportional to a current flowing through the drive transistor flows. The current detection circuit detects the current flowing through the sense transistor, thereby enabling to detect with high accuracy the current (more specifically, the current flowing between the drain and the source of the drive transistor) flowing through the drive circuit.